The clinical term for middle ear infections is otitis media (OM). According to Klein, Vaccine, 19 (Suppl. 1): S2-S8, 2000, OM is the most common reason for an ill child to obtain healthcare and for a child in the United States to receive antibiotics or undergo a general anesthetic. Statistics indicate that 24.5 million physician office visits were made for OM in 1990, representing a greater than 200% increase over those reported in the 1980s. While rarely associated with mortality, the morbidity associated with OM is significant. Hearing loss is a common problem associated with this disease, often affecting a child's behavior, education and development of language skills (Baldwin, Am. J. Otol., 14: 601-604, 1993; Hunter et al., Ann. Otol. Rhinol. Laryngol. Suppl., 163: 59-61, 1994; Teele et al., J. Infect. Dis., 162: 685-694, 1990). The socioeconomic impact of OM is also great, with direct and indirect costs of diagnosing and managing OM exceeding $5 billion annually in the U.S. alone (Kaplan et al., Pediatr. Infect. Dis. J., 16: S9-11, 1997).
OM is thought to result from infectious, environmental and host genetics factors. Bacteria such as Haemophilus influenzae, Streptococcus pneumoniae and Moraxella catarrhalis are the most common infectious organisms in OM. Acute OM is a disease characterized by rapid onset and short duration of signs and symptoms of inflammation in the middle ear, while chronic OM refers to a condition that is defined by the relatively asymptomatic presence of fluid (or effusion) in the middle ear. However, in chronic OM, despite the absence of certain signs of acute infection (i.e., ear pain or fever), these abnormal middle ear fluids can persist for periods exceeding three months. Treatment of acute OM by antibiotic therapy is common, but antibiotic-resistant bacteria have emerged. Surgical management of chronic OM involves the insertion of tympanostomy tubes through the tympanic membrane of the ear while a child is under general anesthesia. While this procedure is commonplace (prevalence rates are ˜13%; Bright et al., Am. J. Public Health, 83(7): 1026-8, 1993) and is highly effective in terms of relieving painful symptoms by draining the middle ear of accumulated fluids, it is invasive and carries incumbent risks (Berman et al., Pediatrics, 93(3):353-63, 1994; Bright et al., supra.; Cimons, ASM News, 60: 527-528; Paap, Ann. Pharmacother., 30(11): 1291-7, 1996). There is thus a need for additional approaches to the management and, preferably, the prevention of OM.
OM vaccine development is most advanced for S. pneumoniae, the primary causative agent of acute OM (AOM), as evidenced by the recent approval and release of a seven-valent capsular-conjugate vaccine, PREVNAR® (Eskola and Kilpi, Pedriatr. Infect. Dis. J. 16: S72-78, 2000). While PREVNAR® has been highly efficacious for invasive pneumococcal disease, coverage for OM has been disappointing (6-8%) with reports of an increased number of OM cases due to serotypes not included in the vaccine (Black et al., Pedriatr. Infect. Dis J, 19: 187-195, 2000; Eskola et al., Pedriatr. Infect. Dis J., 19: S72-78, 2000; Eskola et al., N. Engl. J. Med., 344: 403-409, 2001; Snow et al., Otol. Neurotol., 23: 1-2, 2002).
H. influenzae is a gram-negative bacterium that, as noted above, plays a role in OM. Clinical isolates of H. influenzae are classified either as serotypes “a” through “f” or as non-typeable depending on the presence or absence, respectively, of type-specific polysaccharide capsules on the bacteria. A vaccine for H. influenzae type b has been developed. Like Prevnar®, the type b H. influenzae vaccines target the polysaccharide capsule of this organism and thus the vaccine is comprised of capsule polysaccharide that has been conjugated to a protein carrier. Less progress has been made for a vaccine for non-typeable H. influenzae (NTHi) which causes approximately 20% of acute OM in children and predominates in chronic OM with effusion (Coleman et al., Inf and Immunity, 59(5), 1716-1722, 1991; Klein, Pedriatr. Infect. Dis J., 16, S5-8, 1997; Spinola et al., J. Infect. Dis., 154, 100-109, 1986). NTHi can also cause pneumonia, sinusitis, septicemia, endocarditis, epiglottitis, septic arthritis, meningitis, postpartum and neonatal infections, postpartum and neonatal sepsis, acute and chromic salpingitis, epiglottis, pericardis, cellulitis, osteomyelitis, endocarditis, cholecystitis, intraabdominal infections, urinary tract infection, mastoiditis, aortic graft infection, conjunctivitis, Brazilian purpuric fever, occult bacteremia and exacerbation of underlying lung diseases such as chronic bronchitis, bronchietasis and cystic fibrosis. A prototype NTHi isolate is the low passage isolate 86-028NP which was recovered from a child with chronic OM. This strain has been well characterized in vitro (Bakaletz et al., Infect. Immun., 53: 331-5, 1988; Holmes et al., Microb. Pathog., 23: 157-66, 1997) as well as in a chinchilla OM model (Bakaletz et al., Vaccine, 15: 955-61, 1997; Suzuki et al., Infect. Immun., 62: 1710-8, 1994; DeMaria et al., Infect. Immun., 64: 5187-92, 1996). The NTHi strain 86-026NP was deposited with the American Type Culture Collection, 10801 University Blvd., Manassas, Va. 20110, on Oct. 16, 2001 and assigned accession no. PTA-4764. A contig set from the genome of stain 86-028NP can be found at http://www.microbial-pathogenesis.org.
Adherence and colonization are acknowledged first steps in the pathogenesis of H. influenzae. As such, H. influenzae express multiple adhesions including hemagglutinating pili, fimbriae and non-fimbrial adhesions (Gilsdorf et al., Pediatr Res 39, 343-348, 1996; Gilsdorf, Infect. Immun., 65, 2997-3002, 1997; and St. Geme III, Cell. Microbiol., 4, 191-200, 2002). Notably, none of the adhesions described have previously been associated with a motility function. Moreover, H. influenzae do not express flagella with are also associated with motility. Twitching motility is a flagella-independent form of bacterial translocation over moist surfaces and occurs by extension, tethering, and then retraction of polar structures known as type IV pili (Bardy, Microbiology, 149, 295-304, 2003; Tonjum and Koomey, Gene, 192, 155-163, 1997; Wolfgang et al., EMBO J., 19, 6408-6418; Mattick, Annu. Rev. Microbiol., 56, 289-314, 2002). Type IV pili are typically 5-7 nm in diameter, several micrometers in length and comprised of a single protein subunit assembled into a helical conformation with 5 subunits per turn (Bardy et al., Microbiology, 149, 295-304, 2003; Wall and Kaiser, Mol. Microbiol., 32, 1-10, 1999). Type IV pilin subunits are usually 145-160 amino acids in length and may be glycosylated or phosphorylated. There are two classes of pilin subunits, type IVa and type IVb, which are distinguished from one another by the average length of the leader peptide and the mature subunit, which N-methylated amino acid occupies the N-terminal position of the mature protein, and the average length of the D-region (for disulfide region). Most of the respiratory pathogens express class IVa pilins, whereas the enteropathogens more typically express class IVb pilins. Type IVa pili are distinguished by the presence of a highly conserved, hydrophobic N-terminal methylated phenylalanine.
Type IV pili serve as a means of rapid colonization of new surfaces. Thus type IV pilus expression is important to both adherence and biofilm formation by many bacteria (Mattick, Annu. Rev. Microbiol., 56, 289-314 2002; O'Toole and Kolter, Mol. Microbiol., 30, 295-304, 1998; Klausen et al., Mol. Microbiol., 50, 61-68, 2003; Jesaitis et al., J. Immunol., 171, 4329-4339, 2003), as well as virulence of Neisseria species, Moraxella bovis, Vibrio cholerae, enteropathogenic Escherichia coli and Pseudomonas aeruginosa, among others (O'Toole and Kolter, supra; Klausen et al., supra; Klausen et al., Mol. Microbiol., 48, 1511-1524, 2003; Strom and Lory, Annu. Rev. Microbiol., 47, 565-596, 1993). A biofilm is a complex organization of bacteria that are anchored to a surface via a bacterially extruded exopolysaccharide matrix. The matrix envelopes the bacteria and protects it from the human immune system. Ehrlich et al., JAMA, 287(13), 1710-1715 (2002) describes biofilm formation by H. influenzae. It has been postulated that blocking the interaction between type IV pili and the human body can avoid or stop the bacterial infection (Meyer et al., U.S. Pat. No. 6,268,171 issued Jul. 31, 2001).
Type IV pilus expression is a complex and highly regulated bacterial function. In P. aeruginosa, the biogenesis and function of type IV pili is controlled by over forty genes (Strom and Lory, supra). To date, only a subset of the vast number of related type IV pilus genes (Tonjum and Koomey, supra; Darzins and Russell, Gene, 192, 109-115, 1997) have been found in several members of the HAP (Haemophilus, Actinobacillus and Pasteurella) family (Stevenson et al., Vet. Microbiol., 92, 121-134, 2003; Doughty et al., Vet. Microbiol., 72, 79-90, 2000; Dougherty and Smith, Microbiology, 145, 401-409 1999), but neither expression of type IV pili nor twitching motility has ever been described for any H. influenzae isolate. In fact, H. influenzae is classically described as a bacterium that does not express these structures (Friedrich et al. Appl. Environ. Microbiol., 69, 3695-3700, 2003; Fussenegger et al., Gene, 192, 125-134, 1997), despite the presence of a cryptic gene cluster within the strain Rd genome (Fleischmann et al., Science, 269, 496-512, 1995). Strain Rd is a non-encapsulated derivative of an H. influenzae serotype d organism (Zwahlen et al., Infect. Immun., 42, 708-715, 1983; Bendler and Goodgal, J. Microbial., 70, 411-422, 1972; Risberg et al., Eur. J. Biochem., 261, 171-180, 1999). Although strain Rd has some virulence properties, serotype d strains are generally considered to be commensals; they do not frequently cause disease (Daines et al., J. Med. Microbiol., 52, 277-282, 2003). It is therefore important to make the distinction between disease-causing strains of H. influenzae and strain Rd.